I really admire what Justin and Ian have produced and have experimented with both. I prefer Hybrid over Thematic but that might be a personal preference as both are great products.
The question though was about Genesis. I've been using it since beta and absolutely love it. It's totally changed the way that I and people I contract with do business.
1. Incredible support
2. SEO goodness, no need for a plugin and the upcoming SEO features in 1.3 are well thought out and based on expert SEO advice.
3. The framework has been run through a security audit by Mark Jaquith
4. Clean code, flexible structure
5. Built-in multiple layouts
6. Automatic updates
7. Well thought out theme settings
8. Lots of hooks
9. A couple of great plugins - Simple Sidebar and Simple Hooks plugins
10. Many Child Themes to choose from and easy to create your own
11. Great selection of built-in widgets (I love the featured post widget)
I feel confident using and recommending Genesis
Disclaimer :-) Brian Gardner has been very gracious to accept and sell a couple of basic business child themes I designed for Genesis.
Tapping a Keg of WordPress